This invention relates to hot melt adhesives which exhibit a controllable open time. In particular, this invention relates to hot melt butene-1 homopolymer and butene-1-ethylene copolymer adhesives.
Adhesive open time which we are referring to is the maximum time at which adhesion (adhesion to itself or to a substrate) can take place for material after it is cooled from the melt to room temperature. Hot melt adhesives which exhibit a long open time (greater than 20 minutes), as well as good cold metal bonding, have long been sought for various applications which require a long open time. For example, expansive surfaces to be coated by adhesives such as table tops to which formica is bonded or assembly line auto parts which are coated with adhesive or sealant and later contacted with other parts at some point further down the assembly line are particularly suited to the use of hot melt adhesives which display long open times. Sometimes adhesive coated parts must remain uncontacted for as long as several hours, and thus, require longer open times than are exhibited by and characteristic of polymers typically used in nonpressure sensitive hot melt adhesives.
Hot melt adhesives can be formulated to be pressure sensitive and have an infinite open time but these adhesives are usually soft, tacky and have limited strength and adhesion. Conventional hot melts such as formulations of poly(ethylene/vinylacetate), polyethylenes, polyamides, or polyesters are rigid, form good strong bonds to certain substrates but have short open time usually less than 1 minute. Moreover, these adhesives usually have problems in adhering to cold metal substrates which is often required for automotive applications.
Solvent applied contact adhesives can be formulated to give good bond strengths and reasonable open times but they require the use of solvents which can be toxic, a pollutant and/or a fire hazard. The polybutylene adhesives are unique in that they require no solvents, have long open times, and show improved adhesion to cold metal substrates.
The butene-1 homopolymer and copolymers are a unique group of olefinic polymers because of their slow crystallization rate. The very slow crystallization rate of butene-1 homopolymers and copolymers, in contrast to the crystallization rate of other crystalline polymers such as EVA, polyethylene and polypropylene, have been found to be beneficial in formulating novel hot melt adhesives which have very long open times as well as good adhesion and bonding to cold, heat-sink type substrates (metals, such as stainless steel and anodized aluminum).
The addition of a nucleating agent will increase the rate of crystallization of butene-1 homopolymer and copolymers. This has been found beneficial in the formulation of hot melt adhesives where the open time can be tailored to the application.